Very high speed digital subscriber line receiver, and programmable gain amplifier and narrow-band noise remover thereof

ABSTRACT

A very high digital subscriber line (VDSL) receiver, and a programmable gain amplifier (PGA) and a narrow-band noise remover thereof. The VDSL receiver includes: a first programmable gain amplifier (PGA) for controlling gain to output a signal having a predetermined amplitude and amplifying the input signal according to the controlled gain; a narrow-band noise remover for detecting the narrow-band noise from the output signal of the first PGA, modeling the narrow-band noise to remove the noise from the output signal of the first PGA if the narrow-band noise is detected, and outputting the inherent output signal of the first PGA if the narrow-band signal is not detected; a second PGA for amplifying the output signal from the narrow-band noise remover based on the gain controlled by the first PGA if narrow-band noise exists, and outputting the inherent output signal of the narrow-band noise remover without amplification if narrow-band noise is not detected; an equalizer for compensating for the deteriorated characteristics of the output signal from the second PGA; and a slicer for converting the output signal of the equalizer into a digital signal. Thus, a desired level of the input signal can be maintained against sudden inflow of an external interference signal, so that error generated by sudden change in power can be prevented. Accordingly, a VDSL system adopting the receiver can function normally regardless of inflow of a high-power signal.

This application claims priority under 35 U.S.C. §§119 and/or 365 to98-16786 filed in Korea on May 11, 1998; the entire content of which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a very high speed digital subscriberline (VDSL) receiver, and a programmable gain amplifier (PGA) and anarrow-band noise remover thereof, and more particularly, to a VDSLreceiver for controlling gain during reception of a signal includingnarrow-band noises, and a PGA and a narrow-band noise remover thereof.

2. Description of the Related Art

As the need for information transmission increases, there has been muchresearch conducted to find a method for transmitting data at high speed.In particular, research has concentrated on a method utilizingconventional telephone lines to transfer information at a high speed.

VDSL is a technology for transferring data at a high speed tosubscribers over conventional telephone lines eliminating the need forselection of a specific pair of lines and which does not requireparticular conditions or a redesign of the conventional telephone lines.In the VDSL, data streams consist of high-speed data 20 such ascompressed video data, going toward subscribers from an informationsource, and high-speed data such as a control signal, going toward theinformation source from the subscriber.

A VDSL system, as shown in FIG. 1, comprises a VTU-O (VDSL TransmissionUnit at the Optical Network Unit) 100 for transmitting data tosubscribers and receiving data from the subscribers, and a VTU-R (VDSLTransmission Unit at the Remote Location) 102 connected through achannel to the VTU-O, for transmitting data to the information sourceand receiving data therefrom. During data transmission through thechannel between the VTU-O 100 and the VTU-R 102, AWGN (Additive WhiteGaussian Noise) and narrow-band noise intrudes.

The AWGN refers to the noises distributed over a wide frequency bandwith a relatively small amplitude, and narrow-band noise refers to thenoises generated at a narrow frequency band with a high amplitude andcausing serious errors to a s receiving site. The narrow-band noise canbe in the form of an RFI (Radio Frequency Interference) or an impulsivenoise. RFI is signal interference from ham radio communications.According to the characteristics of the RFI, generation of such signalsis not continuous. That is, the signals are randomly generated ordisappear over several milliseconds to several seconds. Also, thegenerated signal occupies an arbitrary frequency band, thus it is amajor interference factor compared to a general broadcast wave. On theother hand, in the case that impulsive noise is generated when afluorescent lamp is turned on, its interference duration lasts severalmicroseconds, which is too short and thus negligible.

FIG. 2 is a block diagram of a conventional VDSL. The VDSL comprises anautomatic gain controller (AGC) 200, an equalizer 202 and a slicer 204.

The conventional VDSL of FIG. 2 operates as follows. The AGC 200controls the power of an input signal to a desired level, and theequalizer 202 compensates for deteriorated characteristics of the signaloutput from the AGC 200. The slicer 204 converts the output of theequalizer 202 into a digital value according to a threshold value.

FIG. 3 is a detailed block diagram of the AGC 200 of FIG. 2. The AGC 200comprises a multiplier 300, an analog-to-digital converter (ADC) 302, amean square calculator (MSC) 304, an adder 306, an integrator 308 and again regulator 310.

The AGC 200 operates as follows. First, the multiplier 300 multipliesthe input signal by a feedback gain-controlled value. The ADC 302converts the output of the multiplier 300 into a digital signal andoutputs the digital signal. The MSC 304 calculates the mean power to theoutput signal of the ADC 302. The adder 306 calculates the differencebetween the mean power and a reference power level, and the integrator308 integrates the output of the adder 306, which is for making thesignal insensitive to surrounding noises. The gain regulator 310compares the output of the integrator 308 with a threshold value tooutput a gain control value according to the comparison back to themultiplier 300.

The main function of the above-described AGC is to provide a desiredpower level to the input signal. Thus, the requirements of a device suchas a synchronizer which requires an input signal to be a predeterminedstep size or belong to a predetermined dynamic range of a receiving sitemay be not satisfied. Also, the conventional AGC controls the gains to apredetermined amplitude regardless of surrounding interference signals,so that it cannot cope with sudden changes in power due to majorinterference factors such as RFI. Accordingly, it is not possible toprocess the error generated by a sudden surge or drain of power. Forexample, when only a signal is input during initialization of a system,the AGC controls the gain only based on the input signal. Here, when anRFI signal having a power equivalent to the original signal is inputsuddenly, the power of all signals is doubled. Accordingly, when thesignals pass through the ADC, the original signal is clipped, therebycausing quantization error.

Also, when strong narrow-band noise such as RFI intrudes intotransmission lines, the performance of the conventional receiverdeteriorates. As a result, desired performance of the entire systemcannot be realized, When the amplitude of the narrow-band noise is verylarge, the operation at the receiving site becomes unstable, and the tapcoefficient of an equalizer of the receiving site diverges such thattransmitted data cannot be detected. Also, because no one can predictwhen, at what amplitude and into which frequency narrow band noise willintrude, it is not possible to adaptively remove the narrow-band noise.

SUMMARY OF THE INVENTION

To solve the above problems, it is an object of the present invention toprovide a programmable gain amplifier (PGA) for maintaining theamplitude of an attenuated or distorted signal input to a receiving siteof a very high speed digital subscriber line (VDSL) system at a desiredlevel, narrow-band noise remover for removing narrow-band noises mixedin the input signal, and a VDSL receiver having the same.

According to an aspect of the present invention, there is provided avery high speed digital subscriber line (VDSL) receiver for processingan input signal to which a narrow-band noise is inflowed, for high-speedtransmission, the receiver comprising: a first programmable gainamplifier (PGA) for controlling gain to output a signal having apredetermined amplitude and amplifying the input signal according to thecontrolled gain; a narrow-band noise remover for detecting thenarrow-band noise from the output signal of the first PGA, modeling thenarrow-band noise to remove the noise from the output signal of thefirst PGA if the narrow-band noise is detected, and outputting theinherent output signal of the first PGA if the narrow-band signal is notdetected; a second PGA for amplifying the output signal from thenarrow-band noise remover based on the gain controlled by the first PGAif narrow-band noise exists, and outputting the inherent output signalof the narrow-band noise remover without amplification if narrow-bandnoise is not detected; an equalizer for compensating for thedeteriorated characteristics of the output signal from the second PGA;and a slicer for converting the output signal of the equalizer into adigital signal.

According to another aspect of the present invention, there is provideda programmable gain amplifier (PGA) for controlling a gain to amplify aninput signal, comprising: a multiplier for multiplying the input signalby a feedback signal; an analog-to-digital converter (ADC) forconverting the output of the multiplier into a digital signal, andoutputting the digital signal; a peak detector and averager fordetecting peak values among a predetermined number of sampled signalsoutput from the analog-to-digital converter, and calculating the averageof the peak values; a multi-threshold detector for outputting a signalindicating a change in gain to its first output end, and a signalcontrolling a step size of the gain to its second output end, accordingto the output of the peak detector and averager; and a gain regulatorfor determining the step size according to the output signal of thesecond output end of the multi-threshold detector, and controlling thegain according to the determined step size and the output signal of thefirst output end, to output the controlled gain to the multiplier.

According to still another aspect of the present invention, there isprovided a narrow-band noise remover for removing a narrow-band noisefrom an input signal to which a narrow-band noise is inflowed,comprising: a first delay for delaying the input signal by apredetermined period; an adaptive filter for modeling the delayedsignal; a switch controller for determining that the narrow-band noiseis inflowed if the output value of the adaptive filter is higher than apredetermined level, and turning on a switch to output the output valueof the adaptive filter; and an adder for subtracting the output value ofthe adaptive filter, input when the switch is turned on, from the inputvalue.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings in which:

FIG. 1 is a block diagram of a very high speed digital subscriber line(VDSL) system;

FIG. 2 is a block diagram of a conventional VDSL receiver;

FIG. 3 is a detailed block diagram of the automatic gain controller(AGC) of FIG. 2;

FIG. 4 is a block diagram of a VDSL receiver according to the presentinvention;

FIG. 5 is a block diagram of the first PGA of FIG.4;

FIG. 6 illustrates the operation of the peak detector and averager ofFIG. 5;

FIG. 7 shows the output values of a first output end of themulti-threshold detector according to the output value of the peakdetector and averager of FIG. 5;

FIG. 8 shows the output values of a second output end of themulti-threshold detector according to the output value of the peakdetector and averager of FIG. 5

FIG. 9 is a detailed block diagram of the narrow-band noise remover ofFIG. 4;

FIGS. 10A through 10C show an input signal to a conventional AGC and thefirst PGA according to the present invention and output signalstherefrom;

FIGS. 11A through 11D illustrate the change in total gain by theconventional AGC and the first PGA according to the present invention;

FIG. 12 is a graph showing signal-to-noise ratios (SNRs) of equalizersin a conventional receiver and a receiver according to the presentinvention; and

FIGS. 13A through 13F show constellations of the equalizers in theconventional receiver and in the receiver according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 4, a very high speed digital subscriber line (VDSL)receiver according to the present invention includes a firstprogrammable gain amplifier (PGA) 400, a narrow-band noise remover 402,a second PGA 404, an equalizer 406 and a slicer 408.

The VDSL receiver of FIG. 4 operates as follows. The first PGA 400maintains the amplitude of an input signal at a desired level. Thenarrow-band noise remover 402 determines whether or not a narrow-bandnoise exists in the input signal from the output signal of the first PGA400. If narrow-band noise exists, the narrow-band noise remover 402removes the narrow-band noises. Otherwise, the narrow-band noise remover402 passes the output signal of the first PGA 400 as it is. The secondPGA 404 controls the gain of the output signal 404-3 of the narrow-bandnoise remover 402 based on a signal 404-2 indicating whether or not thenarrow-band noise has been removed. That is, if the output signal 404-3is a low power signal which is the resulting signal after thenarrow-band noise is removed in the narrow-band noise remover 402, thegain of the output signal 404-3 is amplified to an appropriate level inconsideration of the gain of the signal 404-1 output from the first PGA400. Meanwhile, in the case when the narrow-band noise remover 402outputs the signal without removal of the narrow-band noise, the secondPGA 404 passes the signal without amplification such that the amplitudeof the signal is maintained at a predetermined level. The equalizer 406compensates for the deteriorated characteristics of the output signal ofthe second PGA 404, and the slicer 408 converts the output of theequalizer 406 to a digital value according to a threshold value.

As shown in FIG. 5, the first PGA 400 includes a multiplier 500, an ADC502, an absolute value calculator (ABS) 504, a peak detector andaverager 506, a multi-threshold detector 508 and a gain regulator 510.

The multiplier 500 multiplies the input signal by a feedback signal. TheADC 502 converts the output signal of the multiplier 500 into a digitalsignal and outputs the digital signal. The absolute value calculator 504calculates the absolute value of the digital signal. The reason why theabsolute value is calculated is that the output signal of the ADC 502must exist within a predetermined level of amplitude instead of beingcontrolled to a predetermined power level. For example, if a squaredvalue is utilized to maintain a predetermined power level-a numbergreater than 1 becomes larger while a number less than 1 becomessmaller. Thus, it is favorable to utilize the absolute value.

The peak detector and averager 506 sets windows to the output of theabsolute value calculator 504, detects peak amplitudes of the sampleswith each window, and calculates the average of the peak values on eachwindow. Detecting the peak values is for securing a stable output of thefirst PGA, which operates within a predetermined amplitude level. Thesize of the windows may vary. The larger the window is, the more stablethe operation of the first PGA is and the longer the period forconvergence is. Also, calculating the average of the peak values of eachwindow is for making the output of the first PGA less sensitive tonoise. The number of windows for calculating the average of the peakvalues is determined in consideration of the relationship between eachpeak value and the average power. FIG. 6 illustrates the operation ofthe peak detector and average 506 in case there are 32 windows each ofwhich consists of 128 samples.

The multi-threshold detector 508 detects the level of the output of thepeak detector and averager 506 to control the gain to be fed back intothe multiplier 500, and outputs predetermined values respectively tofirst and second output ends according to the detected level. Forexample, if the output of the peak detector and averager 506 is equal toor greater than a first threshold value, the multi-threshold detector508 outputs −1 to the first output end, and if the output of the peakdetector and averager 506 is less than a second threshold value, themulti-threshold detector 508 outputs +1 to the first output end. Also,if the output of the peak detector and averager 506 is a value betweenthe first and second threshold values, the multi-threshold detector 508outputs 0 to the first output end. FIG. 7 illustrates the relationshipbetween the output values (·) of the peak detector and averager 506 andthe output value to the first output end.

A control signal for controlling the step size of the gain is output tothe second output end. For example, when the value output to the firstoutput end is changed from a positive (+) value to a negative (−) value,the multi-threshold detector 508 outputs −1 to the second output end.When the output of the peak detector and averager 506 is equal to themaximum value of analog-to-digital-converted bits by the surge ofnarrow-band noises, or the output of the peak detector and averager 506suddenly drops to a level lower than 3 dB of the maximum value of theanalog-to-digital converted bits by the sudden drain of the narrow-bandnoises, the multi-threshold detector 508 outputs +1 to the second outputend. If the output of the peak detector and averager 506 is equal to orless than a third threshold value, and is equal to or greater than afourth threshold value, the multi-threshold detector 508 outputs −2 tothe second output end. In other conditions, the multi-threshold detector508 outputs 0 to the second output end. FIG. 8 illustrates therelationship between the output values (·) of the peak detector andaverager 506 and the output value to the second output end.

The gain regulator 510 regulates the gains using the values output fromthe first and second output ends of the multi-threshold detector 508,and outputs the regulated gains to both the multiplier 500 and thesecond PGA 404. The gains are regulated according to the followingEquation (1).

gain(n+1)=gain(n)+output value of the first output end of themulti-threshold detector*gain step size  (1)

In Equation (1), n refers to the n^(th) sampling.

The gain step size is determined by the control signal input from thesecond output end of the multi-threshold detector 508. For example,assuming that the gain step size is set to 1.6, 0.8 or 0.4, the gainstep size is lowered by one step from the current step size when thecontrol signal is −1. When the control signal is +1, the gain step sizeis maximized to 1.6 for rapid adaptation. Also, when the control signalis −2, the gain step size is minimized to 0.4. The gain control based onthe gain step size is for detecting change in power of the input signal,caused by a sudden interference of an external signal, therebypreventing errors which may be generated during the analog-to-digitalconversion. For example, when the maximum value of the analog-to-digitalconverted bits is output from the multiple-threshold detector 508, whichmeans that a clipping error is generated by the inflow of thenarrow-band noises, it is preferable to control the gain to a lowervalue. Also, when the narrow-band noise which has increased receptionpower suddenly disappears, so that the level of the reception power israpidly lowered, it is preferable to control the gain to a high valuesuch that the output of the receiver is maintained at a predeterminedlevel. When the output value of the multi-threshold detector 508 is avalue between the third and fourth threshold values, which indicates astable state, the gain step size is minimized to accurately follow thesignal.

As shown in FIG. 9, the narrow-band noise remover 402 includes a firstdelay 900, an adaptive filter 910, a switch 920, a switch controller 930and an adder 940.

In the narrow-band noise remover 402, the first delay 900 delays thetransmitted signal by a predetermined period τ. Here, the delay period τrefers to the period during which auto-correlation of a VDSLtransmission signal is very small while the auto-correlation of anarrow-band noise is very large, which is determined as follows. TheVDSL transmission signal occupies a wide band width compared to thenarrow-band noise, so that the transmission signal has a very lowcorrelation compared to the narrow-band noise. That is, the input signalis the sum of a signal having a very high correlation and a signalhaving a very low correlation. Here, the narrow-band noise is removed byextracting the high-correlation signal from the input signal. Anauto-correlation function R_(xx)(τ) with respect to a signal x(t) is asindicated in the following Equation (2).

 R _(xx)(τ)=E[x(t)x(t+τ)]  (2)

The delay period τ is determined by the Equation (2). The signal delayedby τ in the first delay 900 is modeled through the adaptive filter 910which is a kind of finite impulse response filter.

In the adaptive filter 910, the signal is delayed by a plurality ofdelays D each by a predetermined period T, each delayed signal ismultiplied by a tap coefficient C_(n) (n=0, . . . , N−1), and the sum ofthe products is calculated. The weight C_(n) is updated using theStochastic Gradient Algorithm represented by the following Equation (3),such that the difference between the input signal and the final outputsignal of the adaptive filter 910 decreases.

C _(n)(k+1)=C _(n)(k)−μe _(k) r(kT−nT)  (3)

In the Equation (3), the terms are defined as follows:

C_(n)(k): tap coefficient of the n^(th) tap at the time kT;

μ: step.size for updating the tap coefficient;

r(t): output signal of the first delay 900;

e_(k): z(k7)−r(kT); and

z(kT): output of the adaptive filter 910 at the time kT.

The switch controller 930 determines that the narrow-band signal ismixed if the amplitude of the output signal from the adaptive filter 910is greater than a predetermined value, turns on the switch 920, and thenoutputs a switch-on signal indicating the ON-state of the switch 920 tothe second PGA 404 (see FIG. 4). On the contrary, if the amplitude ofthe output signal from the adaptive filter 910 is smaller than thepredetermined value, the switch controller 930 determines that thenarrow-band signal is not input, and then turns off the switch 920.

When the switch 920 is turned on, the adder 940 subtracts the outputvalue of the adaptive filter 910 from the signal input from the firstPGA 400 (see FIG. 4), to output the signal from which the narrow-bandnoise has been removed to the second PGA 404.

The second PGA 404 stores the input gains, which are determined by thegain regulator 510 of the first PGA 400, for a predetermined period insequence, and compares the gain stored a predetermined period earlierwhen the switch 920 is turned on according to the switch-on signal inputfrom the switch controller 930, with the gain after a predeterminedperiod passes from the turning on of the switch 910. The second PGA 404controls its own gain according to the gain difference before and afterthe switch 920 is turned on, to maintain the amplitude of thepower-lowered signal whose power is lowered due to the narrow-band noiseat an appropriate level. In order to prevent the tap coefficients of theequalizer 406 from diverging during determination of the gains, it ispreferable that the tap coefficients are not updated during apredetermined period after the switch 920 is turned on.

Also, when the switch 920 is turned off, the second PGA 404 determinesthat the narrow-band noise is not applied or disappears, and controlsits own gain to 0.

FIGS. 10A through 13F illustrate the difference of simulation resultsbetween the prior art and the present invention. Here, the desiredoutput level was set to 2. Also, 16 CAP (Carrierless Amplitude and PhaseModulation) signals having a sampling frequency of 51.84 MHz, as atransmission signal, are transmitted through 26 AWG 1 Kft channel, and11 FEXT (Far End Crosstalk) was added to the transmission signal, suchthat the gain required for the desired output level would be 20 dB.Then, an RFI signal having a central frequency of 10 MHz and the samepower as that of the input signal was generated, input to the each PGAfor a predetermined period, and then removed. Then, the performances ofthe PGA and the VDSL receiver were measured. Also, variable gain stepsizes of the first PGA were 1.6, 0.8 and 0.4 dB.

FIGS. 10A through 10C comparatively show the output signals of theconventional AGC and the first PGA according to the present invention.In detail, FIG. 10A shows a signal to be input to the conventional AGCand the first PGA according to the present invention, to which thenarrow-band noise is applied. For the result of FIG. 10A, the inputsignal was generated using 16 CAP signals and a radio frequencyinterference (RFI) signal having a power level higher than the inputsignal by 3 dB was then applied to the input signal. Here, thenarrow-band noise was introduced at the 80,000^(th) sampling and thenremoved at the 160,000^(th) sampling. FIG. 10B shows the output signalfrom the conventional AGC and FIG. 10C shows the output signal from thefirst PGA according to the present invention. As shown in FIG. 10B, whenthe gain is updated by applying the narrow-band noise, the amplitude ofthe output signal from the conventional AGC far exceeds the intendedamplitude ±2, so that the output signal is relatively unstable. On thecontrary, the output signal of the first PGA according to the presentinvention is stable within the intended amplitude range of ±2 when thefirst PGA reaches a steady state as shown in FIG. 10C. Thus, the firstPGA according to the present invention can reduce erroneous intervalscaused by the narrow-band noise such as an RFI, compared to theconventional AGC.

In case the first PGA of the present invention is applied to an actualVDSL system, the gain updating by the gain regulator of the first PGAdoes not continue; rather gain updating stops after the output valueconverges on a steady state, and the gain regulator operates only whenthere is a sudden inflow of the narrow-band signal from the outside. Asa result, the load on the entire system can considerably be reduced.

FlGS. 11A and 11B show amplitude of the error signal and total gain bythe conventional AGC according to the number of updatings when thesignal of FIG. 10A is input. Every updating is performed on 32×128samples, and reference numerals 1100 and 1101 represent first and secondthreshold values, respectively. As shown in FIGS. 11A and 11B, theconventional AGC cannot respond rapidly to sudden surge of thenarrow-band signal after it output signal reaches the steady state, sothat it is difficult to expect rapid change of gain. As a result, asaturation error is generated through the analog-to-digital conversionduring the inflow of the noise, thereby deteriorating the overallperformance of the system. Also, perturbations of gain continue evenafter convergence on the steady state, thereby lowering stability.

FIGS. 11C and 11D show the peak average and the total gain by the firstPGA according to the present invention according to the number ofupdatings when the signal of FIG. 10A is input. Here, reference numerals1103 and 1104 represent third and fourth threshold values. First, it canbe understood from FIG. 11C that it takes less time to reach the steadystate compared to the conventional case shown in FIG. 10A. Also, changein gain is rapid when the narrow-band signal is applied after the outputsignal reaches the steady state. As a result, most output valuesconverge on the steady condition, and the first PGA responds rapidly tosudden disappearance of the narrow-band noise, thereby minimizingdistortion of the input signal.

FIG. 12 is a graph showing signal-to-noise ratios (SNRs) of equalizersin the conventional VDSL receiver and the VDSL receiver according to thepresent invention. Here, reference numeral 1200 represents the SNR ofthe VDSL receiver according to the present invention, and referencenumeral 1201 represents the SNR of the conventional VDSL receiver. Asshown in FIG. 12, the VDSL receiver according to the present inventionshows a stable SNR when the narrow-band noise is present. Also, theequalizer according to the present invention rapidly converges after thenoise disappears.

FIGS. 13A through 13F show constellations of the equalizers in theconventional VDSL receiver and the VDSL receiver according to thepresent invention. In detail, FIGS. 13A and 13B show constellations ofthe equalizers of the receiver according to the present invention andthe conventional receiver, respectively, when the narrow-band noise isnot present, i.e., up to the 80,000^(th) sampling. FIGS. 13C and 13Dshow constellations of the equalizers of the receiver according to thepresent invention and the conventional receiver, respectively, when thenarrow-band noise is present, i.e. during 80,000 samplings through the160,000^(th) sampling. FIGS. 13E and 13F show constellations of theequalizers of the receiver according to the present invention and theconventional receiver, respectively, after the narrow-band noisedisappears. As can be understood from FIGS. 13A through 13F, in the caseof using the conventional receiver, its operation is very unstable whenthe narrow-band noise is present and disappears, so that theconventional equalizer cannot operate normally. Meanwhile, the operationof the receiver according to the present invention is stable.

As described above, in the VDSL receiver according to the presentinvention, first, a desired level of the signal can be maintained evenwhen an external interference signal suddenly appears, so that errorgenerated by a sudden change in power, and malfunction of the system bythe sudden surge of a high-power signal can be prevented. Also, the VDSLreceiver according to the present invention can actively cope withnarrow-band noise as described above, and an impulse noise can benegligible in this receiver. Thus, the overall performance of the VDSLsystem can show improved resistance to external interference.

Second, the output of the amplifier can be maintained within apredetermined range against a variable input signal, and the average ofpeak values of a predetermined interval is used as a control signal, sothat the gain can faithfully be controlled with respect to thetransmitted signal.

Third, the step size is controlled for gain control, so that the inputsignal can reach the steady state within a short time, and accuratelyfollow the input signal after reaching the steady state. Thus, the VDSLreceiver can rapidly cope with the sudden change in power of the inputsignal.

Fourth, the narrow-band noise inflowed to the original transmissionsignal at a specific band is removed, thereby preventing interferencefrom the narrow-band noise.

Fifth, problems relating to convergence by the equalizer, such as delayin the convergence, which occurs when a high-power narrow-band noise isapplied or disappear, can be prevented.

What is claimed is:
 1. A very high speed digital subscriber line (VDSL)receiver for processing an input signal to which a narrow-band noise isinflowed, for high-speed transmission, the receiver comprising: a firstprogrammable gain amplifier (PGA) for controlling gain to output asignal having a predetermined amplitude and amplifying the input signalaccording to the controlled gain; a narrow-band noise remover fordetecting the narrow-band noise from the output signal of the first PGA,modeling the narrow-band noise to remove the noise from the outputsignal of the first PGA if the narrow-band noise is detected, andoutputting the inherent output signal of the first PGA if thenarrow-band signal is not detected; a second PGA for amplifying theoutput signal from the narrow-band noise remover based on the gaincontrolled by the first PGA if narrow-band noise exists, and outputtingthe inherent output signal of the narrow-band noise remover withoutamplification if narrow-band noise is not detected; an equalizer forcompensating for the deteriorated characteristics of the output signalfrom the second PGA; and a slicer for converting the output signal ofthe equalizer into a digital signal.
 2. The very high speed digitalsubscriber line (VDSL) receiver of claim 1, wherein the first PGAcomprises: a multiplier for multiplying the input signal by a feedbacksignal; an analog-to-digital converter (ADC) for converting the outputof the multiplier into a digital signal, and outputting the digitalsignal; a peak detector and averager for detecting peak values among apredetermined number of sampled signals output from theanalog-to-digital converter, and calculating the average of the peakvalues; a multi-threshold detector for outputting a signal indicating achange in gain to its first output end, and a signal controlling a stepsize of the gain to its second output end, according to the output ofthe peak detector and averager; and a gain regulator for determining thestep size according to the output signal of the second output end of themulti-threshold detector, and controlling the gain according to thedetermined step size and the output signal of the first output end, tooutput the controlled gain to the multiplier.
 3. The very high speeddigital subscriber line (VDSL) receiver of claim 1, wherein thenarrow-band noise remover comprises: a first delay for delaying theoutput signal of the first PGA by a predetermined period; an adaptivefilter for modeling the delayed signal; a switch controller fordetermining that the narrow-band noise is inflowed if the output valueof the adaptive filter is higher than a predetermined level, and turningon a switch to output the output value of the adaptive filter; and anadder for subtracting the output value of the adaptive filter, inputwhen the switch is turned on, from the input value.
 4. The very highspeed digital subscriber line (VDSL) receiver of claim 3, wherein thesecond PGA stores the gain controlled by the first PGA for apredetermined period, and calculates the difference of the gains storedbefore and after the switch is turned on, to determine its own gainaccording to the gain difference.
 5. A programmable gain amplifier (PGA)for controlling a gain to amplify an input signal, comprising: amultiplier for multiplying the input signal by a feedback signal; ananalog-to-digital converter (ADC) for converting the output of themultiplier into a digital signal, and outputting the digital signal; apeak detector and averager for detecting peak values among apredetermined number of sampled signals output from theanalog-to-digital converter, and calculating the average of the peakvalues; a multi-threshold detector for outputting a signal indicating achange in gain to its first output end, and a signal controlling a stepsize of the gain to its second output end, according to the output ofthe peak detector and averager; and a gain regulator for determining thestep size according to the output signal of the second output end of themulti-threshold detector, and controlling the gain according to thedetermined step size and the output signal of the first output end, tooutput the controlled gain to the multiplier.
 6. The programmable gainamplifier (PGA) of claim 5, wherein the peak detector and averagerdetects the peak values on the absolute values of the outputs from theanalog-to-digital converter.
 7. The programmable gain amplifier (PGA) ofclaim 5, wherein the gain regulator regulates the gain using thefollowing equation: gain(n+1)=gain(n)+a*b wherein n represents a signalsampled through the n^(th) sampling, a represents the output value ofthe first output end of the multi-threshold detector, and b representsthe step size.
 8. A narrow-band noise remover for removing narrow-bandnoise from an input signal to which narrow-band noise is inflowed,comprising: a first delay for delaying the input signal by apredetermined period; an adaptive filter for modeling the delayedsignal; a switch controller for determining that narrow-band noise isinflowed if an output value of the adaptive filter is higher than apredetermined level, and turning on a switch to output the output valueof the adaptive filter when it is determined that narrow-band noise isinflowed; and an adder for subtracting the output value of the adaptivefilter, input when the switch is turned on, from the input value.
 9. Thenarrow-band noise remover of claim 8, wherein the first delay determinesa delay time for which the auto-correlation of the narrow-band noise ishigh and the auto-correlation of the signals other than the noise islow, using the auto-correlation of the input signal, and delays theinput signal by the detected delay time.
 10. The narrow-band noiseremover of claim 8, wherein the adaptive filter comprises: a pluralityof delays for delaying the output signal of the first delay by apredetermined period; and an adder for multiplying the outputs of eachdelay by each tap coefficient, and calculating the sum of the products.11. The narrow-band noise remover of claim 10, wherein the adaptivefilter updates the tap coefficients such that the difference before andafter passing through the adaptive filter becomes minimal.
 12. Thenarrow-band noise remover of claim 8, wherein the first delay employs anauto-correlation function R _(xx)(τ)=E[x(t)x(t+τ)] wherein x(t) is theinput signal and τ is the delay.
 13. The narrow-band noise remover ofclaim 8, wherein the adaptive filter includes a plurality of delayelements, wherein each of said delay elements delays the signal by apredetermined period T and each delayed signal is multiplied by a tapcoefficient C_(n)(n=0, . . . , n−1), wherein the weight C_(n) is updatedusing the stochastic gradient algorithm as follows C _(n)(k+l)=C_(n)(k)−μe _(k) r(kT−nT) wherein the terms are defined as follows:C_(n)(k): tap coefficient of the n^(th) tap at the time kT; μ: step sizefor updating the tap coefficient; r(t): output signal of the firstdelay; e_(k): z(kT)−r(kT); and z(kT): output of the adaptive filter atthe time kT.